Formula of square

- (a + b)
^{2 }= a^{2}+2ab+b^{2}

- (a – b)
^{2 }= a^{2}-2ab+b^{2}

- a
^{2}-b^{2 }= (a + b) (a – b)

- (x + a) ( x + b) = x
^{2}+ (a + b)x+ a b

- (a + b +c)
^{2}= a^{2 }+ b^{2}+ c^{2}+ 2ab + 2bc + 2ca

Corollary

- a
^{2}+ b^{2}= (a + b)^{2}-2ab - a
^{2}+ b^{2}= (a – b)^{2}+2ab - (a + b)
^{2 }= (a – b)^{2}+ 4ab

- (a – b)
^{2}= (a + b)^{2}– 4ab

- a
^{2}+b^{2 }+c^{2}= (a + b + c)^{2}– 2(ab + bc + ca) - 2(ab + bc + ca) = (a + b + c)
^{2}– a^{2}+b^{2 }+c^{2}